1. Field of the Invention
The present invention relates to an air conditioning system. More particularly, the present invention concerns pretreating makeup air being supplied to an air conditioning unit.
2. Description of the Prior Art
In a typical air conditioning system having a vapor compression refrigeration circuit various components such as a compressor, condenser, evaporator and expansion device are arranged to transfer heat energy between a fluid in heat transfer relation with the evaporator and a fluid in heat transfer relation with the condenser. In a heat pump system an outdoor coil and an indoor coil are located such that the compressor through a reversing valve may direct hot gaseous refrigerant to either coil acting as a condenser. The other coil then acts as an evaporator such that, depending upon the position of the reversing valve, heat energy is either rejected or absorbed in both the indoor coil or the outdoor coil. In the heating mode of operation, heat is rejected in the indoor coil acting as a condenser and heat is absorbed at the outdoor coil acting as an evaporator. The reverse is true in the cooling mode of operation wherein the heat is rejected in the outdoor coil acting as a condenser and heat is absorbed in the indoor coil acting as an evaporator.
It is known in the air conditioning industry to provide an air conditioning unit which is suitable for being mounted on the roof or by the side or some other location next to an enclosure to be conditioned. This unit is typically divided into an indoor section having an indoor heat exchanger and an outdoor section having an outdoor heat exchanger. An indoor fan is mounted within the indoor section for supplying conditioned air to the enclosure. This indoor fan draws this air both from the enclosure as return air and from ambient air as makeup air. The air entering the indoor section is passed in heat exchange relation with the indoor heat exchanger wherein either the heat is absorbed from the air flowing therethrough or heat is rejected to said air. Consequently, the air being supplied to the enclosure is conditioned within the indoor section of the air conditioning unit.
The outdoor section of the unit is arranged such that heat energy may be transferred between the outdoor heat exchanger and the ambient air flowing therethrough. Typically, an outdoor fan is provided to circulate the air through the outdoor heat exchanger. The compressors of the typical system are located within the outdoor section.
Under some operating conditions a relatively high amount of makeup air is required. Particularly in fast food operations having a large grease utilization within the enclosure makeup air may amount to as much as 50% of the supply air to the enclosure. With a high percentage of makeup air required and when the ambient conditions are extreme, it has been found helpful to precondition the makeup air. Makeup air is preconditioned to achieve several effects. Firstly, the capacity of the air conditioning unit (not including preconditioning unit) may be decreased if the makeup air being supplied thereto is preconditioned to either raise or lower its temperature. This sizing decrease may result in a cost reduction in the manufacture of the unit. Additionally, by preconditioning makeup air the air conditioning unit whether in the cooling mode or the heating mode is more efficient since the makeup air has already had its temperature raised or lowered depending upon the appropriate conditions. Consequently, by preconditioning makeup air there may not only be initial savings in manufacturing costs but by an increase in efficiency there may be additional savings in the operating cost of the air conditioning unit.
Additionally, depending upon the various controls, it may be possible under some ambient conditions to provide complete conditioning of the air with the preconditioning unit. As described herein, the preconditioning unit will have a separate heat pump system for transferring heat energy between the makeup air and the ambient. Under certain conditions this makeup air heat pump may be sufficient to handle the load on the system.